The main purpose of this study is to determine whether the long-term administration of co-enzyme Q (CoQ) , or ubiquinone, retards or accelerates the aging process in mice and to elucidate the underlying mechanisms. CoQ is present in the hydrophobic interior of virtually all the cellular membranes and has versatile functions. It is best known as a component of the electron transport system in the inner mitochondrial membrane, where, in concert with alpha-tocopherol, it also acts as an antioxidant, inhibiting oxidative damage. Paradoxically, auto-oxidation of CoQ is also the main source of mitochondrial superoxide anion radical and H2O2 generation CoQ is being widely consumed by humans as a dietary supplement, even though the effects of long-term intake of CoQ are virtually unknown. Whether the long-term intake of CoQ leads to an attenuation or an exacerbation of oxidative stress has not been determine. The present study will elucidate the nature of biochemical and behavioral perturbations following the administration of exogenous CoQ10 to mice. The specific hypothesis to be validated or refuted is that "CoQ administration will decrease the level of oxidative stress, improve and preserve mitochondrial respiratory functions, enhance motor and cognitive performance, and extend life span of mice." Specific Aims include determination of the effects of CoQ administration on: (1) the longevity of mice; (2) age-associated changes in mitochondrial respiratory functions and oxidative damage; (3) perturbations of homeostasis among the main anti-oxidative defenses; (4) age-related accrual of oxidative damage to lipids, proteins and DNA in tissue homogenates; and (5) age-associated decline in cognitive and motor abilities of the mice. Results of this study will provide an understanding of the mechanisms by which CoQ intake may have a beneficial or deleterious effect on the aging process in mice.